Fastening members such as bolts and nuts are used in various fields so as to fasten and fix materials and parts.
In case that impact and vibration are repeatedly applied to a fastened part fastened by a fastening member, the fastened part will be loosened, thus a modified fastening member having a following structure has been provided.
The fastening member, which fastens a body being fastened by a screw tightening action, comprises: a head section being used to turn the fastening member about an axial line; and a tapered section being concentrically integrated with the head section, extended from a base part of the head section and formed into a cylindrical shape whose diameter is gradually increased toward an extension end and made greater than that of the head section, an inner surface of the tapered section is a cone curved surface, and an outer surface of the tapered section is a concave-curved surface (see Patent Document 1). With this structure, violent vibration and impact can be absorbed, so that the body being fastened can be securely fixed without being loosened.
The fastening members (including washers) such as the above described bolt and nut (hereinafter referred to as “bolt, etc.”) have a common locking structure, e.g., the tapered section (tapered-cylindrical-body-shaped part). A tapered-cylindrical-body-shaped part of a locking nut can be produced by a dedicated machine (e.g., parts former), so it can be inexpensively produced. On the other hand, the tapered-cylindrical-body-shaped part of the locking bolt is produced by metal cutting work, so a production cost must be increased and mass production cannot be performed.
In the tapered-cylindrical-body-shaped part of the fastening member disclosed in Patent Document 1, the entire outer surface of the tapered section is formed into the concave-curved surface, so a peripheral edge part cannot have enough strength and external dimensions cannot be appropriately reduced.
Further, if a ring-width of the ring-shaped seating surface contacting the body being fastened is narrow, sufficient frictional resistance between the seating surface and the body being fastened cannot be obtained, and impact and vibration caused by the body being fastened and tightening force of the bolt, etc. exceed elastic force of the tapered-cylindrical-body-shaped part, therefore the tapered-cylindrical-body-shaped part will be plastic-deformed.